The excellent heat distortion temperature of chlorinated poly(vinylchloride) resins (hereinafter "CPVC" for brevity) predicates their use in applications where poly(vinyl chloride) resins (hereinafter "PVC" for brevity) would otherwise be chosen. CPVC resins are derived by chlorination of PVC, a reaction which has been studied in great detail over the past twenty years or so, during which numerous chlorination processes have been developed. Most preferred is a process carried out by suspending PVC in water, which PVC is swollen with a halogenated lower hydrocarbon swelling agent, and irradiating swollen PVC with ultraviolet light (actinic radiation) while bubbling chlorine gas ("Cl.sub.2 ") into the water. This process is disclosed in U.S. Pat. No. 2,996,489 to Dannis, M. L. and Ramp, F. L. the disclosure of which is incorporated by reference herein as if fully set forth. Several subsequent inventions related to this basic process have been disclosed in the textbooks "Polyvinylchloride und Vinylchloride-Mischpolymerizate", pp 120-125, Springer, Berlin (1951); "Vinyl and Related Polymers," by C. A. Schildknecht (1952); and in U.S. Pat. Nos. 2,426,808; 2,590,651; 3,100,762; 3,334,077; 3,334,078; inter alia. The disadvantage of these liquid-phase processes in which the reaction occurs in an aqueous medium, is that (a) chlorine dissolves in water with difficulty, and even at elevated temperature and pressure, chlorinated product forms relatively slowly; and, (b) it is only with difficulty and expense that essentially all the swelling agent used in these processes can be removed from the CPVC product.
Other chlorination processes use reaction in an inert liquid medium (which liquid does not react with PVC), without a swelling agent, such as those disclosed in German Pat. No. 2,322,884 published Nov. 22, 1973; U.S. Pat. Nos. 3,506,637 and 3,534,013; inter alia.
Still other less preferred chlorination processes using an inert liquid medium comprise dissolving or suspending the resin in a chlorinated hydrocarbon solvent and promoting the reaction with heat, light, or a catalyst. Yet other processes utilize a fluidized bed of PVC which is contacted with Cl.sub.2 gas, optionally diluted with an inert gas, and optionally also containing a lower chlorinated hydrocarbon, again catalyzed by ultraviolet radiation. Such processes have been disclosed in U.S. Pat. Nos. 3,532,612; 3,663,392; 3,813,370; Japanese Pat. No. 49-45310; British Patent Specification Nos. 1,089,323; 1,242,158; 1,318,078; and, German Pat. Nos. 1,110,873; 1,259,573; inter alia. These fluidized bed chlorination processes occur in a gaseous reaction medium, but with difficulty, because of the slow gaseous diffusion of Cl.sub.2 into solid PVC macrogranules. The term "macrogranules" is used herein to define a cluster or aggregate of randomly closely packed primary particles of suspension PVC. A handful of macrogranules has the feel of fine sand, and are also referred to as "grains". A macrogranule of suspension PVC or CPVC will typically have an average diameter of from about 100 to about 150 microns, A preferred size distribution of each macrogranule is in the range from about 50 to about 500 microns, and conventionally ranges from about 100 to about 200 microns. Each macrogranule is made up of a multiplicity of primary particles each in the size range from about 0.05 micron to about 5 microns, and more typically in the range from about 0.5 micron (5000 A) to about 2 microns (20,000 A). The bulk of the primary particles are usually submicronic in size, though conditions of polymerization will determine the actual size distribution of both primary particles, and also, macrogranules. Macrogranules can be characterized by their porosity, that is, internal pore volume, and surface area.
The morphology of PVC and CPVC macrogranules, specifically the porosity and surface area, are important properties which determine the physical properties of an article after the polymer is molded. Since CPVC is generally derived by the chlorination of PVC, it has been found that the properties of product CPVC may be tailored to a large extent by precisely controlling the conditions under which precursor PVC is polymerized. Such a process is disclosed in U.S. Pat. Nos. 3,506,637 and 3,534,103. With care, the internal morphology of PVC macrogranules may be particularly tailored to permit relatively fast chlorination in a fluidized bed process catalyzed by actinic radiation. Even so, it is necessary for economy, to practice the process in two stages, as disclosed in U.S. Pat. No. 4,039,732 to Stamicarbon B. V.
I am aware that it is known to chlorinate solid crystalline polyethylene ("PE") by reacting between 5 to 100 parts of liquid Cl.sub.2 per part of PE, in a reaction medium of liquid Cl.sub.2, until the resulting chlorinated PE (hereinafter "CPE" for brevity) dissolves in the liquid Cl.sub.2, and then to recover CPE by evaporating the Cl.sub.2. This process is described in greater detail in Canadian Pat. No. 471,037 to John L. Ludlow which teaches a process for the chlorination of ethylene polymers. In this process, PE is suspended in at least 5 parts liquid Cl.sub.2 and irradiated with a suitable light source. As taught by Ludlow, the chlorination of PE which is crystalline and has no chlorine bound in its structure, proceeds from the surface inwardly, the chlorinated polymer dissolving in the chlorine substantially immediately upon its formation, thereby exposing unchlorinated polymer. The PE is not homogeneously chlorinated.
Quite surprisingly, however, the chlorination of PVC in liquid CL.sub.2 results in the substantially homogeneous chlorination of the PVC. By "homogeneous chlorination" I mean the chlorination of PVC so that when the Cl content of the CPVC formed is at least 65% by wt, the ratio of residual mols of PVC present as a block or run (sequence) of at least 3 vinyl chloride ("VC") units, to the mols of total VC units is less than 0.30. This may be stated as follows: ##EQU1## Homogeneity of CPVC having a Cl content of at least 65% by wt uniquely characterizes the CPVC produced by the process of this invention. This homogeneity is attributed to the presence of Cl throughout the PVC polymer. The presence of Cl on the backbone allows the PVC to swell in liquid Cl.sub.2 sufficiently to form a gel phase which allows rapid reaction. In other words, Cl.sub.2 produces a gel phase in the PVC, swelling it without producing a solution of PVC in Cl.sub.2. Thus, CPVC produced in my invention is a G-product quite distinct from CPVC resins prepared in solution ("solution chlorinated") and referred to as L-product (see "Encyclopedia of PVC" edited by Leonard I. Ness, Chapter 6 "Chemically Modified Polyvinyl Chloride", p 229). PE is not chlorinated by a gel type chlorination. Though PE and PVC may each be chlorinated in liquid chlorine, many polymers of monoolefinically unsaturated monomers are not chlorinated in liquid Cl.sub.2, or only slightly chlorinated. For example, poly(vinyl fluoride), and poly(vinylidene chloride-vinyl chloride, 88:12) are not chlorinated; and, as Ludlow taught, unless PE is suspended in at least 5 parts by weight liquid Cl.sub.2, there is very little chlorination.
In my copending patent application Ser. No. 177,969 filed Aug. 14, 1980, there is disclosed a process for the relatively dry chlorination of PVC macrogranules in which only sufficient liquid Cl.sub.2 is used as will "wet" the macrogranules without any visual appearance of having been "wetted". The terms "wet" and "wetted" are used therein to refer solely to the presence of liquid Cl.sub.2 on macrogranules of polymer, and not to the presence of water. When the requisite amount of liquid Cl.sub.2 within a narrowly specified range is absorbed by the solid PVC which is then irradiated with actinic (ultraviolet) radiation, there results a reaction in the solid PVC medium which produces a CPVC product which is distinguishable over prior art CPVC products formed by prior art methods. In this "relatively dry chlorination of PVC" the reaction proceeds in a solid medium, the liquid Cl.sub.2 having diffused into the solid PVC without affecting its free-flowing nature.
I am unaware of any process for the chlorination of PVC macrogranules by a reaction which occurs in a gel phase in a suspension of PVC in liquid Cl.sub.2. It is the peculiar characteristic of such a reaction which results in the substantially homogeneous chlorination of the PVC.
It is reported to be possible to obtain "uniform chlorination" of PVC in water (see Takadono, Yoshido and Fukawa in Kogyo Kagaku Zasshi, Vol. 67, No. 11, 1928 (1964); C.A. 62, 13262h), but this requires the assumption that Cl.sub.2 is a solvent for PVC and that Cl.sub.2 will thus enter even the most crystalline regions (see "Encyclopedia of PVC" supra, p 228). A homogeneously chlorinated PVC prepared in a suspension of PVC in hydrochloric acid is also reported by Seidel, Singer and Springer in Ger.(East) Pat. No. 32586; (C.A. 63, 7130f). In each case, the light-catalyzed reaction was of extremely long duration, about 8 hours. Since my reaction proceeds very rapidly despite being a gel type chlorination, it is clearly a distinctly different process.
It should also be noted that in U.S. Pat. No. 2,996,489 it is stated that the CPVC made therein has "a structure in which at least 75%, more preferably at least 95%, and most preferably essentially all (i.e. 97-98%) of the chlorinated vinyl chloride units are 1,2-dichloroethylene units. Such products are thus distinguished over prior art CPVC resins which contain a significantly higher proportion (i.e. greater than 10%) of the chlorinated vinyl chloride units as the undesirable 1,1-dichloroethylene units" (see top of col 2). This statement was based on chemical analysis of the CPVC prepared by using chloroform and other hydrochoromethylene compounds as swelling agents in the 2,996,489 process. At that time, pulsed Fourier transform .sup.13 C nuclear magnetic resonance ("Cnmr" for brevity) spectra were not available, and the details of the structure of CPVC revealed through analysis of the spectra were not known. The Cnmr spectra presented herewith provide an insight into the structure of prior art materials as well as those prepared by the high liquid chlorination process of this invention. Comparison of these spectra graphically highlights their similarities and differences. Analyses of the spectra are based on studies such as those described in "Determination of Tetrad Concentration in Poly(vinyl chloride) Using Carbon-13 Nuclear Magnetic Resonance Spectroscopy" by Carman, Charles J., in "Macromolecules", Vol 6, pg 725 et seq, Sept-Oct 1973.